What are Metrology & Measuring Tools?

What is Metrology Equipment?

Metrology equipment, also known as metrology tools or metrology measuring instruments, is the collection of calipers, micrometers and gauges that engineers use to measure a part and prove it matches the drawing and Accu's metrology range brings all of them together in one place. On a bench, the hand-held instruments are easy to spot by their sliding jaws or C-shaped frame and spindle, read from a vernier scale, a dial or a digital display, while fixed gauges such as threaded plugs, threaded rings and plain cylindrical plugs are solid steel with no moving parts at all. Between them, they turn a tolerance on a drawing into either a precise number or a clear pass or fail, so a nonconforming part is caught at inspection rather than at assembly.

Much of the range is built to recognised dimensional standards, including DIN 862 for calipers, DIN 863 for micrometers, ISO 1502 for metric thread gauges and DIN 7150-2 for plain plug gauges. That makes it well suited to industrial metrology in aerospace, automotive and motorsport, medical device manufacture and general machining, where measurement results often have to stand up to a customer audit.

How Metrology Equipment Works.

Precision metrology relies on two different principles. Calipers and micrometers are variable instruments that return a number: a caliper's jaws slide along a graduated beam and the gap between them is read from a vernier scale, a rack-driven dial or an electronic encoder. A micrometer advances its spindle on a precision thread, typically 0.5 mm per turn on metric models, so each turn can be divided into steps as fine as 0.001 mm, while a ratchet stop or friction thimble applies the same measuring force every time. Fixed gauges return a verdict instead: the Go end must enter or screw onto the feature and the No-Go end must not, which proves the feature sits inside its tolerance band without anyone having to interpret a scale.

Consider a machined aluminium bracket that mounts a flap actuator to an aircraft wing spar. Before it's released, an inspector checks the flange thickness with an outside micrometer, the hole centres and overall length with a digital caliper, the pivot bore with an H7 plain plug gauge and each M8 tapped hole with a Go/No-Go plug thread gauge. A bore outside its H7 limits would leave the pivot bush either loose or impossible to press home and an oversized thread could let a bolt strip under actuator load. The same routine, with different parts on the bench, verifies a motorsport suspension upright, an automotive gearbox casing or the bores of a medical infusion pump housing.

Materials Metrology Equipment Is Made From

Accu's metrology measuring equipment is made from engineering materials selected for dimensional stability, wear resistance and dependable performance in everyday workshop use:

• Stainless Steel: The standard material for caliper beams and jaws and for many micrometers, resisting corrosion from coolant and handling while holding its form through repeated use.
• Steel: Used for thread gauges, plain plug gauges and some micrometer frames, with the plain plug gauges hardened to HRC 60 +/-2 so their gauging surfaces resist wear.
• Plastic: A lightweight choice for a digital caliper intended for general workshop checks, where an accuracy of +/-0.1 mm is sufficient.
• Steel - (C45): A medium carbon steel used for the smaller rack gauges, offering good strength and machinability.
• Steel - Chromoly - SCM435: A chromium molybdenum steel that responds well to heat treatment, used on the coarser rack gauges.
• Steel - Chromoly - SCM436: A second chromium molybdenum grade, also used on the coarser rack gauges.

Selected calipers and micrometers also add harder contact faces for high-volume or abrasive work:

• Carbide Tipped Jaws: Caliper jaws tipped with carbide, which resist wear far better than stainless steel when measuring hardened or abrasive parts.
• Ceramic Tipped Jaws: Hard, non-magnetic ceramic tips that resist wear and will not attract fine ferrous swarf.
• Carbide Tipped Faces: Micrometer anvil and spindle faces tipped with carbide to keep them flat and parallel through repeated contact.

Sizes & Types of Metrology Equipment Available

Accu's metrology products are available in a wide choice of types and measuring capacities to suit inspection tasks from the toolroom to the production line:

• Calipers: Vernier, dial and digital formats with a Range (Max) of 70 mm to 300 mm, graduations down to 0.01 mm and accuracy down to +/-0.02 mm.
• Micrometers: Outside micrometers with a Range of 0 mm to 175 mm and inside micrometers from 5 mm to 100 mm, in analogue, mechanical counter and digital versions with graduations down to 0.001 mm.
• Plug Thread Gauges: Thread Size M1 to M150 in metric coarse and fine pitches, plus unified, BSW, BSF, BSP, NPT and PG threads, in Go, No-Go and Go/No-Go formats.
• Ring Thread Gauges: Thread Size M1.4 to M150 across the same main thread families.
• Plain Plug Gauges: Gauge Size 2 mm to 100 mm, all to Tolerance Class H7 in a Go/No-Go format.
• Rack Gauges: Pitch 0.5 MOD to 3 MOD with a Face Width (FW) of 8 mm to 30 mm, used to align the joint between two lengths of gear rack.

The ranges do not overlap evenly. Inside micrometers stop at 100 mm and outside micrometers at 175 mm, so larger bores and diameters are a job for a caliper. Every plain plug gauge is made to H7, so bores toleranced to any other class need a different gauge. Most ring thread gauges are sold as individual Go or No-Go rings rather than pairs, so a full check of an external thread needs one of each. Calipers and micrometers are supplied with a certificate of conformity, while JBO Johs Boss thread gauges are available uncalibrated or with JBO calibration certification and are suitable for UKAS calibration on enquiry.

For a gauge or measuring fixture that is not a catalogue item, Accu's custom manufacturing service can produce components to your drawing, from a single prototype to full-scale production.

FAQ

Q: What does metrology mean?

A: Metrology is the science of measurement: defining units, realising them in reference standards and applying them so that a measurement taken in one place agrees with the same measurement taken anywhere else. Metrology and measurement are often used interchangeably, but in engineering the term usually refers to dimensional measurement, meaning the work of confirming that a part's sizes, features and threads match its drawing. For a fuller introduction, read Accu's guide, What Is Metrology?

Q: What are the three main types of metrology?

A: The three main types are scientific, applied and legal metrology. Scientific (or fundamental) metrology establishes the units of measurement and the primary standards behind them, work carried out in the UK by the National Physical Laboratory. Applied, or industrial, metrology puts those standards to work in manufacturing through instrument calibration, process control and part inspection. Legal metrology regulates measurements that affect trade, health and safety, such as retail scales and fuel dispensers. Every product in Accu's metrology range belongs to industrial metrology.

Q: What are common measurement tools?

A: The metrology instruments found in most engineering workshops are calipers for fast general measurement, micrometers for finer external and internal dimensions and fixed gauges, such as thread plug, thread ring and plain plug gauges, for quick pass or fail checks. Inspection rooms often add height gauges, dial indicators, gauge blocks and coordinate measuring machines (CMMs) for more complex work. Accu's range focuses on calipers, micrometers and fixed gauges, which handle the everyday dimensional checks carried out on machined components.

Bespoke Metrology & Measuring Tools Manufacture.

High precision, bespoke manufacture of Metrology & Measuring Tools to customer specification. State of the art facilities specializing in both small batch prototyping and large scale manufacture.